7x17 film storage

I just developed my first 7x17 negatives and hadn't thought about it. What does everyone put these in to store them? I have lots of different plastic that will work but worry that some type might react in a naughty way. Maybe some type of paper envelope?
Thanks for any help.

I got some black foam core material and glue and gaffer's tape and made some nice black boxes to fit each negative size. It took about 20 minutes per box. I just put the sleeved negatives in the boxes. I left a little space on one dimension so that I can attach little post-it tabs with some cryptic identification code written on them to the ends of the sleeves. It helps to locate a particular negative occasionally. I only tab the 'keepers'. The 'yawners' go to the bottom of the pile.